Atlanta Tube Amp
Variac - Why You Should Have One
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Why a Variable Autotransformer "Variac" should be a part of your rig...
Much of this info courtesy of the Premier Guitar article by Peter Stroud (Sheryl Crow, 65 Amps)
Here I address an issue that every guitarist will have to deal with once they step out of the house and into a club.
goes like this: Ever wondered why your
tube guitar amp doesn't sound nearly as good as it does (usually) at home? Haven’t you experienced those times when
the sound is fuzzy, anemic or just plain lifeless? You might even be hearing all sorts of loud buzzes and hums that you attribute to "the stage lights" or something,
particularly with your single coil pickups.
idea of using a variac is to keep the voltage constant from night to night, show to show.
1. General Radio
The important thing to note when buying a variac is its current rating. But you might ask, is that 2A (amps), 5A or 10A? The math is easy, but it’s important.
For instance, how many guitar amplifiers and effects will you be plugging in? A quick guide is to check the VAC fuse value
of your guitar amplifier(s.) If it’s a 3A fuse rating, then most likely your amplifier draws around two amps of current
when pushed. If you're running two guitar amplifiers at the same time, you might be pushing four to six amps of current at
peak points. Pedals and pedalboards usually draw very low amounts of current. You might get by just fine with a variac rated
at 5A current output. So, 7.5A or 10A current output should cover most any need. Go beyond than that and the physical size
of the variac becomes an issue, as well as the price.
WARNING! YOU HAVE TO BE CAREFUL USING VARIACS! If you accidentally hit the knob and boost the voltage up toward 140VAC, you stand the chance of sending your rig to Mars… or at least to the repair shop with a lot of burned-out components and tubes. Hopefully the VAC fuse will blow instead. It’s also possible to cause damage if you're running it at way too low a voltage. Again, the intention here is to have your rig running at its proper voltage!
The answer is to use your ears. Most new guitar amplifiers like to see 117VAC to 120VAC. Most modern amps are wired for 120VAC power. Most homes these days show 119-121VAC coming out of the wall socket. Most stages might get up to 118VAC on a good day but will otherwise be lower, which can adversely affect your sound.
WATCH THAT VOLTMETER! If your new variac doesn't have one built in, check the AC output using a voltmeter. HOWEVER, IF YOU DON'T KNOW HOW TO CHECK THE AC VOLTAGE, THEN YOU SHOULDN'T BE DOING THIS IN THE FIRST PLACE.
Still with me, good.
With a variac, I suggest the following power-up sequence:
Again, if you run your voltage too high, say above 124VAC,
you run the risk of burning components or shortening tube life. Running the voltage too low, say 112VAC or less, can also
cause damage and just won't sound good. The goal here is to run your rig at its proper voltage.
I sell these so if you're ready to get one, contact me. Any variac I have is the right kind for tube amps, will have been checked out and verified to work properly.